This invention relates in general to motor powered overhead garage doors, and in particular to a security timer for automatically closing the garage door after it has been open a selected time interval.
Many residences have overhead garage doors. This type of door rolls on tracks from a closed vertical position to a horizontal position a short distance below the ceiling of the garage. Many of these overhead doors have electric motors for raising and lowering the doors. A manual wall switch will cause the door to open or close. Also, many have a radio receiver for causing the door to open or close. A small transmitter is carried in the automobile for signaling the receiver to open or close the door. This avoids the need for the driver to get out of the car to open and close the door.
One problem with overhead doors is that occasionally they are accidentally left open by the driver. Also, occasionally the radio receiver may receive stray radio frequency signals that cause it to open the door while the resident is away. Electrical power fluctuations may also cause the door to open. Not only does an open door provide access for intruders to the garage, but it also makes it easier for a burgular to break into a door leading from the garage to the house.
There have been a number of proposals for closing and opening doors automatically, such as shown in U.S. Pat. Nos. 3,060,361; 3,510,982; 2,758,836; 1,928,698; 1,874,903; 2,138,521; 2,871,009; and 1,040,504. However, these proposals are generally mechanical in nature and are difficult to implement because they require specially made mechanical parts. U.S. Pat. No. 4,035,702, Petterson et al., discloses an electronic device for closing a garage door after it has remained open for a selected time period. There are disadvantages to this proposal, one of which is that electrical power is continually supplied to the system even though the door is closed. This may result in earlier failure than a system that receives power only when the door is open. Also, there is no provision to vary the time delay between opening and closing. Some users may prefer a different delay than others. Another problem is that the door starts closing without warning. This might result in the door closing on a vehicle or locking a person out of his house.